addons.mozilla.org
Firefox will ping for a version check multiple times during the process of a browser upgrade. The user can manually check for updates as many times as they like. There are weird mis-configured proxies that can spam a single ping a hundred times for some reason, and there are browsers that have been recompiled for a variety of reasons that can behave in a non-standard fashion.
In each of these cases, we do the best we can to eliminate spurious or duplicate requests, but because of NAT and DHCP, we can't really rely much on an IP address to determine the validity of a set of requests.
Personally, I'm happy to provide less accurate statistics and be able to feel good that I am not violating Firefox users' privacy. This extends down to things such as not even storing IP addresses in our data warehouse once the access log data has been parsed. Regardless of the fact we have privacy policies that state we won't do anything bad with the data, I prefer to not even have the data available in a database at all.
Liable for what?
As you said however, who knows what crazy justification they will come up with, and what the courts will buy.
That said, I highly doubt either lawsuit has much of a leg to stand on. Content transformation is a long standing and tacitly accepted feature of web protocols. Caching, zooming, and even assistant technologies such as a screen or braille reader would run afoul this argument.
People don't install adblock when they see an ad for it. They install it when they have been pissed off by intrusive ads once too often.
Hence the main promoter of adblock is the content industry itself with intrusive popup ads, auto-playing audio etc.